The present invention relates to a process and an apparatus to identify the presence of structural cavities in sleeves for the manufacture of driving belts.
The invention is adapted to carry out quality control tests on sleeves for the production of driving belts of different kinds, such as toothed belts, flat grooved belts, toothed V-belts and so on.
In the course of the present description reference will be particularly made, by way of example only, to the test carried out on a sleeve for the manufacture of toothed belts.
It is known that toothed belts are obtained by a cutting operation carried out at several axially spaced circumferential lines on an axially elongated cylindrical tubular sleeve having a toothed inner surface.
This sleeve is made by wrapping at least a reinforcement layer incorporating a plurality of inextensible cords around a cylindrical grooved die which has negatively reproduced toothing on its outer surface and upon which one or more layers of elastomeric material are then superposed.
The semifinished product thus obtained is then submitted to a vulcanization process in an autoclave.
During the above operation the semifinished product, previously enclosed in a rubber coating sheath, undergoes a suitable heating by means of steam under pressure which is sent into the die and to the outside of the sheath surrounding the semifinished product.
Due to the steam pressure, the layers of elastomeric material are submitted to homogeneously-distributed centripetal compressive forces urging the elastomeric material to forcedly pass through the inextensible cord layer. Thus the elastomeric material will fill the grooves provided in the die, thereby creating the inner toothing on the finished sleeve.
It may however happen that, during the vulcanization step, the proper formation of teeth is impaired due to undesired infiltrations of steam and/or condensate between the elastomer layers of the semi-finished product.
These infiltrations give rise to cavities in the sleeve structure and in particular within the teeth and the presence of said cavities causes an alteration to the operating features and strength of the toothed belts that will be subsequently obtained from the above cutting operation.
The formation of cavities can also take place for other reasons, for example due to the development of gas resulting from an incorrect composition of the materials forming the elastomeric layers.
It is clear that when a belt having defects of the above described type is used, it could easily break thereby involving the risk of serious damages to the apparatus on which the belt itself is mounted.
In order to avoid these risks as much as possible, it is necessary that the sleeves produced and/or the belts subsequently obtained be submitted to suitable quality control tests or inspections.
At the present state of the art these inspections are merely based on the visual examination of the toothing by an operator.
As can be easily understood, these empirical inspecting methods offer insufficient reliability. In fact, the identification of possible cavities in the sleeve toothing depends to a great extent on the skill of the operator entrusted with the inspection and the care he or she puts in carrying out the operation.
It is also necessary to take into account the fact that the cavities can be of very small sizes, having a diameter smaller than half a millimeter.
In addition and above all, the mere visual evaluation of the toothed surface enables only cavities appearing on the surface itself to be identified, without offering the possibility of detecting those cavities that are incorporated internally in the elastomeric material.
It is also to be pointed out that the presently used inspection methodologies do not permit timely interventions in the cases in which the structural cavities are due to incorrect operation of the apparatuses used during the sleeve vulcanization step or to errors in the composition of the materials used.
The main object of the present invention is substantially to solve the problems of the known art, by a process and an apparatus enabling an accurate and reliable inspection of the toothing.
A further object of the invention is to provide a process and an apparatus capable of identifying and signalling the presence of structural cavities in the toothing in a very timely manner, when they are due to incorrect operation of the apparatuses adopted in the vulcanization processes or to wrong compositions of the materials used for the manufacture of the sleeves, in order to allow immediate interventions for the elimination of these anomalies.